There is an increasing need to develop new methods and systems to provide isotope separations as the demand for different isotopes increases for industry, science, and medicine. This is particularly true for radioactive isotopes including the various isotopes of the actinide series, such as uranium and plutonium isotopes. With these latter materials, the separation of the respective isotopes, for example, the separation of uranium-238 from uranium-235, is exceedingly difficult to accomplish due to the very similar atomic weights and chemical and physical characteristics of the isotope species. Any separation method or system has to be exceedingly selective in order to provide separation of such isotopes and, to be acceptable, should be economically competitive with other separation systems. General types of isotope separation techniques include gaseous diffusion, centrifugation and laser excitations. Of these, one of the most promising techniques utilizes laser radiation with its very narrow bandwith and high intensity to selectively excite isotopic molecules or atom from ground to excited states and then to separate them by various means from other unexcited isotopic species.
Two laser radiation isotope separation techniques which are currently being used or developed include the metal-laser and molecular gas-laser techniques. In the first, a two-step process is utilized in which a metal containing isotope which it is desired to be separated is volatilized and the vaporized metal then irradiated by one or more lasers to selectively excite one of the isotopes and cause photoionization of that isotope. The ionized isotope may then be trapped to provide an enriched metal output containing the isotope. Such a system has a number of drawbacks including the necessity to generate a signficant concentration of metal atoms in a gaseous phase. In addition, the excitation process requires two or three lasers operating sequentially to provide the desired photoionization and is consequently inefficient and difficult to achieve. Further, since the system utilizes a photoionization process, the technique is relegated to batch operation and is subject to large inefficiencies caused by collisions between the excited and neighboring non-excited species.
Another isotope separation technique utilizes a molecular gaslaser arrangement in which an infrared laser is used to irradiate a molecular gas to cause a selective excitation of a gaseous compound containing a desired isotope. The excited compound may then, by additional photoexcitation with an ultraviolet laser, be decomposed into a nonvolatile product and physically separated from the remaining gas stream. The non-volatile product and the gas stream are then enriched in one or the other of the desired isotopes. This system, like the metal vaporlaser system, requires the use of two or three lasers operating sequentially to induce the desired excitation and decomposition steps, which are inherently inefficient, and at the same time requires very high laser power levels to provide decomposition, at this time laser power levels often beyond the present state of the art. In addition, since the system requires the physical separation of a solid from a gas, it is relegated to a batch operation due to the difficulty of removing the solid from the gas stream without interrupting the flow of materials through the system. Further, exchange collisions between the highly excited species and non-excited species may degrade the purity and efficiency of the technique. In the case of uranium isotope separations where the fraction of uranium-235 in natural uranium is very low, the number of collisions of decomposed product with volatile U-238 molecules would be very high.
It would be desirable to provide a laser-induced isotope separation technique and system which would not require the excitation of the isotope species to a level at which decomposition is required and which would maintain the product in the same form as the source material. It would also be desirable if the laser induced separation technique did not require the use of high temperatures and could utilize a source material in a gaseous form so as to provide a high flow rate capability. It would further be desirable to provide a laser induced isotope separation in which the products are maintained in a gaseous form which may be physically separated without interrupting the flow of gas through the system. In addition, it would be desirable if such a technique could be utilized using relatively low-power, low energy lasers which are presently state-of-the art.